1. Field of the Invention
The subject invention generally pertains to the measurement of pipe used in wells and more specifically to a portable pipe measuring system.
2. Description of Related Art
Oil wells and wells for other fluids typically comprise a string of tubing surrounded by a well casing. The well casing is what lines the wellbore and usually comprises a long string of relatively large diameter pipe interconnected by threaded couplings known as collars. Casings generally define the overall diameter and depth of a wellbore. Well tubing has a much smaller diameter for fitting down inside the casing. Tubing typically comprises a long string of pipe sections whose threaded ends are also interconnected by threaded couplings. The tubing provides a conduit for conveying oil or some other fluid to the surface of the well. Usually a submerged reciprocating pump is attached to the lower end of the tubing to draw the fluid from the annulus between the inside diameter of the casing and the outside diameter of the tubing, and to force the fluid up through the tubing to the surface. To operate the pump, a string of sucker rods extends through the tubing to serve as a long reciprocating connecting rod that couples the submerged pump to a reciprocating drive unit at ground level.
Measuring the length of each casing or tubing segment before installing it down a wellbore can help establish a record of the pipe string's final overall length. This can be accomplished by simply using a tape measure to measure each joint (i.e., measure the length of a pipe segment plus one coupling attached to it) and then recording and summing the readings manually (i.e., manually tallying the readings). To minimize human error, more elaborate electronic measuring methods have been developed, such as those disclosed in U.S. Pat. Nos. 4,701,869; 4,468,959; and 4,234,942. Although electronic methods of measuring provide significant advantages over more traditional methods, such electronic methods have some serious limitations.
The system disclosed in U.S. Pat. No. 4,701,869 comprises a laser connected to a computer. Measurements of the laser go directly to the computer, which then directs a marker to impress the information on the pipe. Having a computer connected to the laser unit greatly limits the system's portability. For instance, when measuring a set of pipes on a rack, instead of moving the laser unit from one pipe to the next, individual pipe segments are rolled onto motor-driven rollers that are controlled by the computer. In some cases, as shown in the patent's FIG. 2, the laser portion of the measuring system is mounted to a more portable fixture (item 5). However, the overall portability of the total system is still limited by still being connected to the computer and is further limited to a target (item 6a) that is constrained to a drilling rig's elevators (item 6). The computer, rollers and/or the drilling rig's elevators can make the '869 system cumbersome and impractical for measuring pipes that are stored in a conventional pipe yard.
A conventional pipe yard is generally a wide-open, outdoor area with numerous pipe racks distributed over several acres. A pipe measuring system tied to a computer means that the computer may have to be lugged around over great distances. Providing electrical power may be a problem with a desktop computer, and the rechargeable battery of a laptop is often limited to just a few hours (due to powering a monitor, internal cooling fan, etc.). Also, bright sunlight can diminish the visibility of a computer screen and is known to damage the screen of many laptop computers. Moreover, rain and extreme outdoor temperatures can be an even greater problem for computers.
A further limitation of the '869 system is illustrated in the patent's FIG. 2. Apparently, both the upper and lower couplings need to be screwed onto the upper pipe in order for the laser measurement system to take a length reading from coupling edge to coupling edge (with compensation for an offset between one coupling edge and the bottom of the elevator). This can interfere with efficient assembling of a pipe string. For instance, a hoist would have to lower the elevators enough to allow the upper pipe to be screwed into the lower coupling, and it appears that the hoist may have to lift the elevators back up again to take up any slack out from between the elevators and the upper coupling.
The measuring system of U.S. Pat. No. 4,468,959 is also a system meant to operate at a generally fixed location, i.e., at a wellbore. Similar to the '869 device, the '959 device also includes a reflector that is attached to a rig's elevators. The system does not appear to be readily adapted for measuring pipes that are lying on a rack.
The measuring system of U.S. Pat. No. 4,234,942 senses the length of a pipe segment through the interior of the pipe. When using such a system, if the length readings of a series of individual pipes are summed to determine a total length of the pipes when interconnected, a significant error may occur by disregarding the length of the couplings or by disregarding the threaded overlap between the couplings and the pipe ends. Also, when relatively long pipes are lying horizontally on a rack, bowing of the pipe may obstruct a clear linear path between opposite ends of the pipe.
Consequently, a need exists for a simple, handheld pipe measuring device that is more reliable than a tape measure and is more portable than current electronic pipe measuring systems.